The prior art has included numerous methods and devices for separating fluids, such as whole blood, into two or more specific components or constituent fractions.
The term "apheresis" describes a three-step procedure wherein whole blood is: (a) withdrawn; (b) separated into two or more fractions; and (c) at least one of the separated blood fractions is retransfused into the patient or donor. The most common type of apheresis procedure is known as "plasmapheresis". In plasmapheresis a quantity of liquid plasma is separated from a "cell concentrate" comprising the remaining liquid and cellular constituents of the blood and such cell concentrate is, thereafter, retransfused into the donor. Other types of apheresis procedures include "leukapheresis" (wherein leukocytes are separated from the whole blood) and "thrombocytapheresis" (wherein platelets are separated from the whole blood). Some apheresis procedures are carried out to effect harvesting and isolation of commercially usable blood components. Other apheresis procedures are carried out for therapeutic purposes. Examples of therapeutic procedures include "therapeutic plasma exchange" (wherein the blood plasma is removed and replaced by a substitute fluid) and various experimental procedures wherein a specific fraction of the blood is isolated and subjected to extracorporeal treatment, such as radiotherapy, chemotherapy, chelation therapy, or adsorptive removal of specific substances by passing the isolated blood fraction through an adsorptive column or the like.
Modern apheresis procedures are typically performed through the use of automated, electronically-controlled, apheresis instruments. Examples of commercially available automated apheresis instruments include the Autopheresis-C.RTM. system (Baxter Healthcare Corporation, Fenwal Division, 1425 Lake Cook Road, Deerfield, Ill. 60015), and the (Haemonetics Corporation, City, State).
In general, the automated apheresis instruments of the prior art utilize one or more extracorporeal blood separation apparatus such as a rotation, membrane or centrifugal separator. Such blood separation apparatus is fluidly connected to a blood vessel of the donor/patient by way of a blood extraction tube. A blood pump, such as a peristaltic pump, is positioned on the blood extraction tube to pump of the whole blood from the donor/patient to the blood separation apparatus. Typically, the blood extraction pump is positioned midway between the point at which blood is withdrawn from the donor/patient (e.g., the venipuncture site) and the point at which the blood enters the extracorporeal separation apparatus (e.g., the inlet). A "distal segment" of the blood extraction tube carries the withdrawn blood from the donor/patient to the blood pump. A "proximal segment" of the blood extraction tube carries the blood from the blood pump to the separation apparatus. In the prior art apheresis instruments, it is common procedure to add a flow of anticoagulant solution (e.g. heparin-saline or warfrin-saline) into the "distal segment" of the blood extraction tube at a location close to the vascular access point. Such addition of anticoagulant solution near the vascular access point serves to prevent clotting or coagulation of the blood as it subsequently passes through the extracorporeal apheresis system. This addition of anticoagulant solution is typically accomplished by providing a bag or container of anticoagulant solution connected to the "distal segment" of the blood extraction tube by way of an anticoagulant solution delivery tube. An anticoagulant pump, such as a peristaltic pump, may be positioned on the anticoagulant delivery tube to pump a metered amount of anticoagulant solution through said anticoagulant delivery tube and into the distal end of the "distal segment" of the blood extraction tube to accomplish the desired anticoagulation effect.
One drawback associated with the practice of adding the anticoagulant solution to the extracted blood at a site within the "distal segment" of the blood extraction tube is that any air bubbles or air inclusions within the anticoagulant feed tube are likely to be drawn directly into the "distal segment" of the blood extraction tube by the drawing action of the blood pump. Such air bubbles or air inclusion will then be carried through the blood pump and into the "proximal segment" of the blood extraction tube. Such air bubbles or air inclusions may then travel through the extracorporeal system until they reach a point at which they are detected, by direct observation, or by way of an electronic air detector located within the extracorporeal system. Such drawing of air bubbles into the system through the anticoagulant delivery tube has been known to occur as a result of inadvertent depletion of the anticoagulant solution within the anticoagulant bag or container. Such drawing of air bubbles through the anticoagulant feed tube may also occur due to inadvertent puncture or disconnection of the anticoagulant feed tube itself.
In view of the adverse effects associated with the above-described inadvertent entrainment of air within the extracorporeal apheresis system, there exists a need in the art for improved methodology and apparatus whereby anticoagulant solution may be effectively added to blood within an extracorporeal apheresis system with minimal or no likelihood of inadvertent entrainment of air bubbles into the extracorporeal system.